1. Modern Truck Electrical Systems
CHAPTER 15
Modern Truck Electrical Systems
Instructor Name: (Your Name)

2. Learning Objectives
Explain the basic functionality of an electronically controlled automatic transmission
Discuss the functionality of an automated manual transmission
Define the terms PRNDL, NSBU, VIM, chuff test, differential braking, and ABS modulator
Explain how an air ABS system and traction control operate

3. Learning Objectives (continued)
Test an ABS wheel sensor circuit
Describe how a fault detected by a trailer ABS ECU causes the trailer ABS warning lamp to illuminate in the truck instrument panel
Discuss the operation of an Eaton electric hybrid system
Discuss the difference between a series hybrid and parallel hybrid truck
List the steps to troubleshoot a wiring problem with the J1939 data link

4. Allison World Transmission
Currently the most common in North America
Full authority control; transmission will only shift when commanded by the transmission ECU
WTEC – World Transmission Electronic Controls
Electronic shift control; no hard line to the transmission
Transmission ECU can use information from the J1708/1587 & J1939 data link

5. World Transmission Controls
Figure 15-2 World transmission components.

6. Allison WT Electronic Shift Selectors
Figure 15-3 Allison WT electronic shift selectors.

7. Allison World Transmission (continued)
WT Transmissions uses 3 reluctance type speed sensors: engine, turbine, and tail shaft
There are two types of solenoids used: normally open and normally closed
Allison Diagnostic Optimized Connection (DOCTM) troubleshooting software
WT Generation 4 can display diagnostic trouble codes on digital display

8. WT Speed Sensors
Figure 15-4 WT speed sensors.

9. WT Solenoids Figure 15-6 WT normally closed solenoid.
Figure 15-7 WT normally open solenoid.

10. WT Hydraulic Schematic – Third Range Setting
Figure 15-9 WT hydraulic schematic – third range attained.

11. Automated Manual Transmissions
AMT – Automated manual transmission
Manual transmission with automatic control
One or two pedal system
Eaton Fuller is currently the most common
Driver interface and transmission ECU communicate via private J1939 network called the EPL

12. Eaton Driver Interface
Figure Eaton driver interface.

13. Automated Manual Transmissions (continued)
Primary inputs to ECU are from three transmission mounted speed sensors and rail select and gear select position sensors
Eaton AutoShift – Three pedal system
Eaton UltraShift – Two pedal system
Eaton ServiceRanger™ is a PC-based EST used to diagnose an Eaton AMT

14. Eaton AMT Speed Sensors
Figure Eaton AMT speed sensors.

15. Gear and Rail Select Position Sensors
Figure Gear and rail select position sensors.

16. Antilock Brake System
Reluctance-type speed sensors on both front and at least two rear wheels on a tandem axle tractor
Typical ABS tone wheel has 100 teeth
The ABS ECU measures the frequency of the waveform produced
ABS modulators control air flow to service brake chambers to prevent brake lock up
Modulators are designed to revert to non-ABS in the event of failure

17. ABS Schematic For Straight Truck
Figure ABS schematic for straight truck.

18. Four Channel ABS With ATC
Figure Four-channel ABS with ATC.

19. ABS Modulator with Integral Relay Valve
Figure Air ABS brake modulator with integral relay valve.

20. Antilock Brake System (continued)
A chuff test is a brief actuation of the modulation coil at start up
A drive axle event can trigger a signal to the transmission and engine ECU or a signal on the J1939 data link
Automatic traction control (ATC) will limit wheel slip under acceleration

21. WARNING
Differential braking can cause a truck to drive off a jack stand if only one drive axle wheel end is lifted off the ground and the driveline is operated. Traction control must also be disabled if truck is operated on a dyno.

22. Advanced ABS Features Steering wheel angle sensor
Air application pressure sensor
Air suspension pressure sensor
Yaw rate sensor
Lateral acceleration sensor
VORAD – Vehicle onboard radar

23. Advanced Air ABS Sensors
Figure Advanced air ABS sensors.

24. ABS Warning Lamp
FMVSS 121 requires an amber-colored ABS warning lamp in clear view of the operator
Three methods of controlling ABS warning lamp:
Direct control by ECU
Control by fail safe relay
Controlled by J1939 data link with a J1939 multiplexed IPC

25. Direct-Wired ABS Warning Lamp
Figure Direct-wired ABS warning lamp.

26. Fail Safe Relay Used to Control ABS Warning Lamp
Figure Direct-wired ABS warning lamp.

27. Diagnosing ABS Systems
Most Meritor-Wabco ABS ECS use warning lamp to retrieve DTCs
Some Bendix systems use a blink code switch
Bendix remote diagnostic unit (RDU) can be plugged into the 9-pin diagnostic connector

28. Blink Codes Displayed Using ABS Warning Lamp
Figure Blink codes displayed using ABS warning lamp flash sequence.

29. Bendix RDU
Figure Bendix remote diagnostic unit (RDU).

30. Trailer ABS
All trailers built after March 1, 1989 are required to have ABS
Power to the trailer ABS is provided through pin 7 of the J560 trailer socket
Trucks and trailer built after March 1, 2001 are required to have a trailer ABS warning lamp on ICP of truck
PLC – Power line carrier

31. PLC Signal Generated by Trailer ABS ECU
Figure Power line carrier (PLC) signal generated by trailer ABS ECU.

32. Tech Tip
A problem with the trailer ABS power supply circuit may cause the trailer ABS warning lamps to flash when the service or trailer brakes are applied.

33. Hydraulic ABS Systems Required on all trucks built after March 1, 1999
Functions similar to air ABS systems
Hydraulic fluid is returned to the reservoir during an ABS event

34. Hydraulic ABS System
Figure Hydraulic ABS system.

35. Hydraulic ABS Disc Brake Rotor
Figure Hydraulic ABS disc brake rotor with cast tone wheel.

36. Hydraulic Power Brakes
Uses two electric pump motors to charge gas filled accumulators with brake fluid under pressure
HCU – Hydraulic compact unit
The HPB system is connected to the J1939 data link
Accumulator pressure is maintained at approximately 2320 psi
If pressure drops below 1523 a low pressure lamp illuminates

37. WARNING
Never attempt to drive a vehicle with HPB that has the brake warning lamp illuminated. You may not be able to stop the vehicle.

38. Hydraulic Power Brakes (continued)
Ignition off, vehicle not moving, service brakes released, unit will go into sleep mode
If ignition is turned on or brake pressed, system will wake and control pump motors as needed
SAHR – Spring-applied hydraulically released parking brake
Meritor-WABCO Toolbox™ is the EST used to diagnose the HPB system

39. WABCO HPB SAHR Park Brake
Figure Wabco HPB spring-apply hydraulic-release (SAHR) park brake.

40. Twisted Wiring for ABS Speed Sensors and Modulators
Figure Twisted wiring for ABS wheel-speed sensors and modulators.

41. Electronic On Board Data Reader (EOBR)
Figure Electronic on-board recorder (EOBR).

42. Satellite Link Between Truck/Trailer and Fleet Management
Figure Satellite link between truck/trailer and fleet management.

43. Hybrid Electric Trucks
Parallel System – Internal combustion engine is supplemented by electric motor
Series System – Truck is propelled only by electric motor and internal combustion engine charges batteries
A three-phase motor/generator is used to propel vehicle and charge batteries
A battery bank with up to 340V DC power and inverter producing up to 500V AC

44. WARNING
Lethal voltage levels are used in hybrid electric systems. You should not attempt to work on the high-voltage components of an HEV until you have had proper training and have all of the proper protective equipment including insulated gloves. High-voltage wiring is identified by orange-colored insulation. Never splice into this high-voltage wiring.

45. Online Service Information Systems (SYS)
Caterpillar Service Information System
Cummins QuickServe Online
Mack Trucks Electrical Information System
Navistar Service Information
Paccar DAVIE and ServiceNet
Volvo IMPACT

46. J1939 Bus Type Network
Figure J1939 bus-type network.

47. J1939 Data Link
Figure J1939 data link modeled as a pair of wires with two 120Ω resistors in parallel.

48. Damaged J1939
Figure Damaged J1939 data link will act as two separate networks.

49. Summary
Allison electronic automatic transmissions use three variable reluctance speed sensors to measure engine, turbine, and output speeds. The transmission ECU controls a series of normally open and closed solenoids using PWM. These solenoids control the flow of transmission fluid to apply clutches for specific ranges.

50. Summary (continued)
Eaton automated manual transmissions (AMTs) use two electric motors to activate the shift mechanism. AMTs are divided into two- and three-pedal systems, indicating if the clutch is controlled by the operator or the transmission ECU. Inputs to the ECU include three speed sensors and rail and gear select positions.

51. Summary (continued)
Air ABS systems use wheel-speed sensors to determine if a wheel lock up is occurring or is about to occur. The ABS ECU then controls modulators to block air flowing to the brake chambers and exhaust air out of the brake chambers to prevent wheel lock up.
Testing wheel-speed sensors and the associated circuits may involve raising each wheel end and rotating the wheel by hand while watching for the amplitude of the AC voltage that is generated by the variable reluctance sensor.

52. Summary (continued)
Trailer air ABS ECUs on modern trucks use the power line carrier technique to signal the truck or tractor ABS ECS that a trailer ABS fault is active. A variable frequency signal is placed onto the 12V power supply by the trailer ABS ECU. This signal is detected by the truck ABS ECU in its 12V power supply, causing the truck ABS ECU to energize the trailer ABS warning lamp on the truck’s instrument panel.

53. Summary (continued)
Electronic on-board recorders (EOBRs) are electronic truck operator log books designed to record the hours of service (HOS) for each truck operator.
In a parallel hybrid system, a diesel engine and electric motor/generator are coupled together. The electric motor is used to supplement the diesel engine. In a series hybrid system, the electric motor alone is used to propel and the engine is used as a generator for the electric motor. A dual-mode hybrid system acts as a series hybrid system during acceleration and a parallel hybrid system at higher speeds.